The present disclosure relates to a magnetic toner for a single component developer.
In electrophotography and the like, in general, a photoconductor obtained by charging with corona charge etc., on a latent image carrier constituted with a photoelectric conductive photoconductor or the like is exposed with laser, LED etc., to form an electrostatic latent image, which is then visualized through developing by a developer such as a toner to obtain an image with high quality. The toners which may be employed in such a development process are usually provided by: mixing a thermoplastic resin as a binder with a colorant, a charge control agent, a release agent, etc.; kneading the mixture; pulverizing and classifying to give toner particles having an average particle diameter of 5 to 10 μm. Furthermore, in order to impart flowability to the toner, to control charge of the toner, and to improve easiness of cleaning of the toner remaining on the photoconductor without being transferred to a recording medium, in general, inorganic or inorganic metal fine powder such as silica or titanium oxide is added to the toner.
At present, known dry development processes in a variety of electrostatography systems which have been put into practical applications include a 2 component development system in which a toner and a carrier such as an iron powder are used, and a magnetic single component development system in which a toner containing a magnetic powder in the toner is used without using a carrier.
Toners containing a magnetic powder for use in magnetic single component development systems (hereinafter, also referred to as magnetic toners) are advantageous in low cost and superior durability; however, they are disadvantageous in that formation of an image having a desired image density is difficult due to lower coloring strength of the magnetic powder as compared with colorants such as carbon black.
In order to overcome such disadvantages in connection with magnetic toners, for example, a positively chargeable magnetic toner which may be used as a single component developer has been provided containing a binder resin and a magnetic powder as principal components, to which a quaternary ammonium salt, a fatty acid metal salt having a metal content of no less than 2.0% by weight and a melting point of 110° C. to 145° C., and a nigrosine dye were added.
However, according to the magnetic toner for a single component developer including a nigrosine dye as the toner described above, favorable charging property is less likely to be achieved when a nigrosine dye is dispersed in a binder resin in a state miscible with the binder resin, and thus formation of favorable image can be difficult. On the other hand, when a nigrosine dye is aggregated and dispersed in a binder resin, due to failure in sufficient coloring of the binder resin with the nigrosine dye, and inferior coloring strength of the magnetic powder, an image having a desired image density is less likely to be obtained.
Also, due to superior fixativity, and ease in homogenous dispersion in the binder resin of the components included in the toner, a polyester resin is often used as the binder resin. However, in magnetic toners contains a polyester resin as a binder resin and a nigrosine dye, the nigrosine dye is aggregated and dispersed in a binder resin, whereby positively chargeable sites are likely to be formed on the surface of the toner. In this case, since the polyester resin is negatively chargeable, the toner particles are likely to be electrically aggregated with one another in low-temperature and low-humidity environments. Therefore, disturbance (layer disturbance) of the thickness of a toner thin layer formed on a developing sleeve is likely to occur in low-temperature and low-humidity environments according to such a toner, leading to a problem of poor image being likely to be generated accompanying with the layer disturbance.
The present disclosure was made in view of the foregoing circumstances, and an object of the present disclosure is to provide a magnetic toner for single component developer that is capable of forming an image having a desired image density, and capable of inhibiting occurrence of layer disturbance in low-temperature and low-humidity environments.